Conventional optical ring networks comprise a plurality of nodes which are linked by optical fibers in a ring-like configuration. The ring may be designed so that data can be transmitted either clockwise or counter clockwise around the ring. Typically, each node comprises a receiver and a transmitter. The transmitter in each node produces a modulated optical signal at a wavelength which can be detected by the receiver at the adjacent downstream node, where downstream is defined as the next node in the direction of data propagation around the ring. Data is transmitted from an originating node to a destination node by passing through each intermediate node on the ring between the originating node and the destination node. At each intermediate node, the data is detected by the receiver and regenerated in optical form by the transmitter.
Various configurations and techniques have been proposed for increasing the transmission rates and capacity of optical ring networks including wavelength division multiplexing (WDM), time division multiplexing (TDM), employing multiple receivers and transmitters in the nodes, and optical ring networks with multiple parallel rings. Although these solutions do increase the capacity of optical ring networks, they are very expensive and can be wasteful of bandwidth.
In a conventional WDM ring, the capacity between a pair of nodes may be increased without making changes to other nodes in the ring, for example by adding additional wavelength channels on a given link. However, a multi-wavelength upgrade generally necessitates a temporary disruption of all traffic on the ring, while optical filters are replaced or added to accommodate the new WDM channels. Furthermore, in a WDM ring a transmitter/receiver pair is required for each connection. Thus, in a N-node ring, N(N−1) transmitter/receiver pairs are needed. As such, if the pairwise demand is below 10 Gb/s (as it often is) such a solution is wasteful in bandwidth and therefore cost ineffective.
For a traditional Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) ring network employing TDM, increasing the capacity between nodes requires upgrading every node in the ring.
Furthermore, for the solutions including multiple receivers and transmitters in the nodes, and optical ring networks with multiple parallel rings, the added components increase the size of the network and add cost to the network. As such, the cost of such a solution scales linearly with the network capacity and therefore there is no economy of scale on a per bit level for larger networks. This is a problem for service providers and a hurdle for building larger networks. Also, if the data demand in a network is significantly less than what the added components can accommodate, the solution provides over-capacity and thus is not cost effective either. As such, an optical ring network is needed with increased capacity that does not increase the size of the network and does not waste available resources.